Process for preparing delustered synthetic fibers and the like



Patented June 25, 1940 PATENT OFFICE PROCESS FOR PREPARING DELUS'I'EBED SYNTHETIC FIBERS. AND THE LIKE George De Witt Graves, Wilmington, Del, assignor to E. I. du Pont de Ncmonrs-& Company, Wilmington, Del, a corporation of Delaware Serial No. 109,181

No Drawing. Application November 4, 1936,

BCIaims. (o1. zoo-s1) This invention relates to shaped artificial objects, and .more particularly to an improved process for making delustered synthetic superpolyamide fibers, sheets. etc.

This invention has as an object animproved method of producing the delustered shaped articles." Another object is a method for making these articles, and particularly fibers, which results in a more complete dispersion of the delustering material throughout the polyamide and hence yields superior products. Other objects will. appear hereinafter.

These objects are accomplished by a process which consists in incorporating the delustering material with the reactant or reactants used in the preparation of the superpolyamide instead of mixing the preformed polymer with the delusterant. Y r

The method of making the fiber-forming polyamides and the fibers therefrom is described in detail in Patents Nos. 2,071,250 and 2,071,253 and Application Serial Number 74,811, filed April 16, 1936, by W. H. Carothers. -These fiber-forming polyamides, are linear condensation products and are made by continued heating under polymerizing conditions of bi-func'tional reactants with removal of the volatile reaction products until the product obtained is capable of being drawn into a filament which may be further cold-drawn (that is, subjected to stress in the solid state) into a useful fiber showing by X-ray examination orientation along the fiber axis. It is to be understood that the term filament as used hereinrefers to both oriented and unoriented fibers or threads which are drawn from the superpolymers regardless of whether the fibers or threads are long (continuous) or short (staple), and that the term "fiber refers more specifically to the oriented fibers which are useful in the manufacture of yarn and cloth .as are natural textile fibers. A valuable property of these superpolyamides is that they can be spun from melt,

that is, by extruding the molten polymer through presence of the delusterant which is-preferably a finely divided material such, as a pigment having a refractive index differing from that of the superpolyamide, is incompatible therewith, and is inert thereto. The term incompatible'is used in the specification and claims to indicate that the finely divided material is insoluble in the superpolyamide at ordinary temperatures and forms a separate phase therefrom. The agent which is added to produce the heterogeneous phase will be referred to as the delusterant. It may be a gas, liquid,- or solid, but preferably it will be a solid. For proper 'delustering' the added agent must;be in a finely divided state and be so distributed throughout the polyamide surface and fiber so as not to impair the continuity of the superpolyamide or destroy its fiber qualities.

The delustered fibers are most advantageously spun from a melt of the polyamide. The present invention is particularly valuable because, as will be pointed out more particularly below, it is difiicult to obtain a good dispersion of the delusterant and molten polymer by methods other thanthat disclosed herein, namely, that of incorporating the delusterant with the monomeric ingredient or ingredients used in the synthesis of the polyamide. The monomeric ingredient or ingredients may be a polymerizable amino acid, an amideforming derivative of a polymerizable-acid, a diamine plus a dicarboxylic acid, a diamine plus an amide-forming derivative of a dibasic carboxylic acid, or a mixture of such ingredients. Other 7 agents such as solvents, non-solvents, plasticizers,

, e. g. o-hydroiwdiphenvl, and viscosity stabilizing agents, e. g. those described in U. S. Patent 2,174,527 may also be present. The polyamideform'ing reactants exert a surprising dispersing action on the delusterant, particularly pigment .delusterants. Thus, it is possible to react a diamine with a dicarboxylic acid or an amideforming derivative of a bibasic carboxylic acid in the present of a pigment, e. g. titanium dioxide, and obtain a superpolyamide in which the pigment is homogeneously dispersed. This homogeneous dispersion is noteworthy for it might be expected that the pigment would tend to flocculate at the high temperature required for polyamide formation or that it would react with the pol'yamide-forming ingredients or adversely affect the polymerization reaction, or that in the abseiice of an added dispersing agent no dispersionwould occur.

It will be noted that the above method for incorporating the deluste'rant into the supermoamldeisquitedlil'erenti'romthatusedinintro- 2 ducing delusterants into cellulosic derivatives.

In the delustering of viscose, for instance, dispersions of pigments are generally prepared by grinding the pigment with water and a dispersing agent or with a 'small portion of viscose, in a ball or colloid mill, and this dispersion is added in the required amount to the main viscose solution. Oils and waxes are emulsified in water and added to the viscose. In delustering cellulose acetate rayon the pigment is generally groundin a dilute solution of cellulose acetate in acetone and this dispersion added to the spinning ter are spun by the preferred procedure, 1. e. melt spinning. The superpolyamides are solids at ordinary temperatures and are frequently so tough that ball mill grinding is accomplished with difliculty. Ball mill or colloid mill grinding methods are also difii'cult to apply to the molten polymers because of their high melting point and high viscosity. Addition of the pigment dispersions in a solvent followed by removal of thesolvent is disadvantageous because of the long time intervals required during which the polymer tends to undergo objectionable transformations. Furthermore, the polymer is so viscous in the molten state that direct addition of the pigment and thorough dispersion thereof are often extremely difficult or impossible. The discovery that the v pigment is thoroughly dispersed in the superpolyamide melt by incorporating it with the monomeric reactants used in preparing the superpolyamide proved very valuable therefore since it furnished a simple and efilcient method for producing delustered superpolyamide products. Mixtures of delusterant and polymer obtained by preparing the superpolyamide in the presence of the delusterant as described above are, partic ularly valuable because they can be readily spun from melt into delustered fibers of good quality. If desired, these mixtures can also be treated with solvent and spun by the wet or dry methods.

As previously pointed out, this invention is best practiced bymaking the fibers from the molten polymer as contrasted with the solution method to which cellulosic materials such as viscose is restricted in theproduction of artificial fibers. Spinning from melt issimpler and more economical than spinning from solution. It will be observed further that methods which involve the incorporation of the delusterant into the superpolyamlde before spinning also differ from the preparation of the known delustered fibers (cellulosic materials) in that the fibers of this invention are stretched or cold-drawn (l. e. subjected to stress while in the solid state) to a much greater degree. The superpolyamide filaments that are extruded from the spinneret are generally cold-drawn from 150 to'600% and are thereby converted into oriented fibers (they exhibit X-ray fiber diflraction patterns which indicate definite orientation along the fiber axis) of high strength and elasticity. It might be thought that this great elongation would restore the luster to the product. In fact, u'nless the filaments contain a sufiicient amount of delusterant,

the fibers do take up a low or subdued luster during the cold-drawing operation. In practice, however, no difi'iculty is encountered in preparing delustered superpolyamide fibers by the process of this invention. The delusterant surprisingly dges not interfere with the cold-drawing opera ion.

. The delusterants used in the practice of this invention must have an index of refraction. which is different, that is, lower or higher, than that of the superpolyamide. The refractive index of most superpolyamides is approximately 1.55. This difference-in refractive index between the delusterant and the superpolyamide should be at least 0.05 and preferably more than 0.2. Th: most useful delusterants, e. g. titanium dioxide, zinc sulfide, and many other pigment-like materials, have indices of refraction which differ from that of the superpolyamides by at least 0.5. Furthermore, the delusterant must be present in the superpolyamide in a finely divided form. This is particularly essential if the delusterant is added before the superpolyamide is spun or other wise there is danger'that the spinneret orifices will become clogged. For the preparation of delustered suprpolyamide fibers the particle size of the delusterant should be less than five microns and preferably less than one micron. If, however, the object to be delustered is a bristle, sheet, film, or molded article, delusterants of larger particle size may be used. For these purposes the particle size may be as large as 25' microns. For the preparation of permanently delustered superpolyamide fibers and fabrics-it is further essential that the delusterant be firmly coated or imbedded in the fiber; it should not be removed by the action of soap, water, or solvents of the type used in dry cleaning. The-delusterant must be inert to the polyamide fiber-forming material and it must be incompatible therewith. In this connection it may be noted that the fiber-forming materials used herein not only difler radically in chemical composition from cellulosic fiber-forming materials but diifer in compatibility characteristics in reactivity toward other agents, the present superpolyamides and cellulosic materials being in fact incompatible with each other. For these reasons agents which have been used in conjunction with cellulosic fiber-forming materials are not necessarily indicated as useful in the production of the new fibrous products described herein.

Inorganic pigment-like materials are especially valuable as delusterants for superpolyamides. These products are in general inert toward the superpolyamides even at the elevated temperatures required for melt spinnig, have a high refractive index, are easily obtained in a finely divided state, .and are not affected by water or solvents. As examples of such materials might be mentioned titanium dioxide, barium sulfate or calcium sulfate extended titanium dioxide, barium titanate, zinc titanate, magnesium titanate, calcium titanate, zinc oxide, zinc sulfide, lithopone, zirconium dioxide, calcium sulfate, barium sulfate, aluminum oxide, thorium oxide, magnesium oxide, silicon dioxide, talc, mica, and the like. Colored materials such as carbon black, copper phthalocyanine pigment, lead chromate, iron oxide, chromium oxide, and ultramarine blue may also be used. Another valuable class of delusterants comprises the non-phenolic polynuclear compounds, such as triphenyl benzene, diphenyl, substituted diphenyls, substituted naphthalenes, and particularly chlorinated compounds of the aromatic and polynuclear type, e. g. chlorinated diphenyl. In general the organic delusterants are lighter and softer than the inorganic pigment-like materials. Various oils, waxes, and resins can also be used, but it is often desirable to use these agents in conjunction with delusterants 01' the types already mentioned.

- The quantity of delusterant used in the preparation of the fibers of this invention will depend upon the nature (degree of dispersion, refractive index, etc.) of the delusterant and upon the degree of opacity desired for the final product. In general, quantities of delusterant ranging from 0.1 to 5.0% by weight of the polyamide are used, when the delusterant is dispersed throughout the fiber. In the case of titanium dioxide, for example, quantities of 0.1 to 2.0 are ordinarily employed. Smaller amounts can be used if the delusterant-is present merely on the surface of the fiber. Quantities of delusterant outside of this range can be used, but the delusterant must not be present in an amount sufiicient to impair the continuity of the superpolyamide or products of inferior flexibility and elasticity will result.

This invention is described more specifically in the following examples in which parts are given by weight: Example I A mixture of 524 parts of hexamethylene diammonium adipate (diamine-dibasic acid salt), 4.72 parts of hexamethylene diammonium acetate (viscosity stabilizer), and 6.75 parts of finely divided titanium dioxide having an index of refraction of approximately 2.54 and particles whose size ranged largely from 0.3 to 0.5 micron in diameter, was placed in a stainless steel autoclave equipped with a stainless steel stirrer and a steam heated reflux condenser wihich in turn was connected through a water cooled condenser to a receiver. The autoclave was evacuated and filled with oxygen-free nitrogen, this process being repeated twice. A pressure of 100 pounds was then-applied by means of oxygen-free nitrogen and the autoclave was heated to 288 C. during two hours. The pressure was then slowly released but the heating was continued for an additional two hours. The stirrer was run ata rate of 16 revolutions per minute during the initial heating period and at a rate of 36 revolutions per minute during the last two hours.

The autoclave was then cooled and the polymer removed as a white, opaque solid. The product had an intrinsicyiscosity of approximately 1.0.

The above sample of'superpolyamida which contained 1.5% of titanium dioxide homogeneous- 1y dispersed throughout, was spun from melt as follows: The polymer-delusterant mixture was extruded at a pressure of 100-125 pounds per sq. in. (applied with oxygen-free nitrogen) at a temperature of 284 C. from a spinneret having 7 orifices. each 0.0078 inch in diameter and placed at the bottom of 0.125 inch cone-shaped protrusions extending downward from the face of the spinneret. The extruded filaments were colwere free from luster and had good dyeing prop erties. 4

' Example II A sample of polyhexamethylene adipamide containing 5% of the dinaphthyl ether of ethylene glycol, prepared by heating hexamethylene diammonium adipate in the presence of 5% of the dinaphthyl ether as described in the preceding example, was spun from melt following the general technique described in Example'l. The polymer had an intrinsic viscosity of 0.8. The delusterant, the above mentioned ether. had three principal indices of. refraction (1.55, 1.65, and 1.80), and a particle size of 1-2 microns.. The spinning conditions (melt process) were as follows: temperature, 284 0.; spinning pressure, 60 pounds per sq. in.; rate of spinning, 634 ft. per min.; extent of cold-drawing, 250%. The delustered fibers obtained in this way had a denier of 4.7, a tenacity of 4.9 g. per denier at break, and

r a residual. elongation of 63%..

Example 11 e The superpolyamide used in this experiment was prepared by heating hexamethylene diammonium adipate containing 1%-of hexamethylene diammonium acetate as viscosity stabilizer, 1.5%

' eral heavy screen packs placed directlyabove the orifices, under the following conditions: spinning temperature, 284 C.; spinning pressure, 125

pounds per sq. in.; spinning rate, 700-900 ft. permin.; extent of cold-drawing, 350%. The delustered fibers obtained in this way had a denier of 3.3, a tenacity at break of 4.93 g. per denier, and a residual elongation of 25%. Yarns and fabrics prepared from these fibers were completely free of luster.-

Other superpolyamides can be delustered by the method given in the above examples. A valuable class 'of delustered superpolyamides comprise those derived from diamines of formula NHzCHzRCHzNHz and dicarboxylic acids of formula HOOCCHzR'CHzCOOH or their amide-forming derivatives, in which R and R'- are divalent hydrocarbon radicals free from olefinic 'or acetylenic unsaturation and in which R has a chain length of at least two carbon atoms. An especially valuable group of superpolyamides within this class are those in which R is (CH2); and R (CHz)y wherein a: and y are integers and a: is at least 2. As examples of superpolyamides which fall within one or both of these groups might be mentioned polytetramethylene adipamide, polytetramethylene suberamide, polytetramethylene sebacamide, polypentamethylene adipamide, polypentamethylene sebacamide, polyhexamethylene adipamide, polyhexamethylene sebacamide, polyoctamethylene adipamide, polydecamethylene adipamide, polydecamethylene sebacamide, polydecamethylene para-phenylene diacetamide, and poly-paraxylylene sebacamide. Polyhexamethylene adipamide, becauseof its high melting point and excellent filmforming qualities,- is a particularly valuable member of this group. Polydecamethylene adipamide is likewise avery valuable product. The present invention is not limited, however, to the use. of superpolyamides of the diamine-dibasic acid type; those derived from 'polymerizable amino acids or their amide-forming derivatives are also readily obtained in the delustered form by the methods herein described. As examples of this type of superpolymer might be mentioned the polymers derived from G-aminocaproic acid (NH:(CH2) :COOH), 9-aminononanoic acid, and

l-l-aminoundecanoic acid. It is within the scope of this invention to prepare delustered shaped articles from mixtures of 'superpolyamides with each other or with other fiber-forming materials.

Delustered articles can also be prepared from interpolymers derived from a mixture of superpolyamide-form'ing reactants, e. g. two diamines polyamide and the resultant mixture is trans formed into a shaped object. By this method the delusterant is dispersed throughout the shaped object more completely and emciently than if the delusterant is incorporated with the preformed polymer or applied to the surface of the shaped object. The method described herein is particularly advantageous because the delustered articles are exceptionally uniform and retain their opacity or low luster even when subjected to abrasion or severe handling conditions.

It may be seen from the foregoing description of the properties which a delusterant must have that a wide variety of compounds can be used as delusterants for superpolyamides.- Numerous pigments and extenders have already been mentioned and their use is specifically illustrated in certain of the examples. Example-11 illustrates the use of an organic delusterant. ,To be effective as a delusterant the organic compound must of course be used in such proportions that it is not compatible with thesuperpolyamides. As additional examples of suitable luster modifying agents which include the preferred materials,

there may be mentioned the following: picene, deca'chlorodiphenyl, hexachlorocarbazole, s-dibenzothiazylmercaptoethane, phenyldinaphthoxanthene, tetraphenyl thiophene, thiodinaphthyl- .amine, di-biphenyl ketone, di-binaphthyl urea,

oxamide, N-di-alpha-naphthylmethane sulfonamide. di-alpha-naphthyl sul'fone, lead formate. the lead salt of N-phenyl phthalamic acid, dialpha-naphthylmethyl phthalate, urea-aldehyde resins,.and polybenzyl resins.

Other materials which may be mentioned as useful for the purpose of this invention are various materials such as the following: bianthryl, tetrachlorodiphenyl, octachloronaphthalene, di-

-naphthyl-p-phenylenediamine, isodinaphthalene oxide, thianthrene, N-phenylcarbazole. dinaphthocarbamle, s-dicarbazyl, 'anilinobenzothiazole,

2-pheny1 benzimidazole. diphenylamine sulfoxide, diphenylamine sulfone. xanthone, anthraquinone, triphenylamine, di-alpha-naphthyl benzamide. diphenyl oxamide, N-di-alpha-naphthyl acetamide, N-tetraphenyl-succinic diamine, 1.3.5

trinaphthalene-sulfonyl benzene, 1,2-dinaphthyl suli'onyl ethane, trimethylene trisulfone,-di-betanaphthyl sulfoxide, barium and calcium salts of benzyl-p-aminobenzoic acid. di-beta-naphthyl succinate, '1,1' di-naphthylmethaneedii'-diben zenesulfonate, phenol-aldehyde resins, polyether resins, and white mineral oil.

75. Not all of the above mentioned compounds,

however, are useful for melt spinning, the materials suitable for this type of spinning are those which are stable at the elevated temperatures used in the process. In general, pigments,

salts, hydrocarbons, chlorinated aromatic hydrocarbons, and related compounds are sufiiciently stable for this purpose.

This invention is also applicable to the preparation ofwdelustered shaped articles from other synthetic linear condensation fiber-forming poly- -mers such as polyethers, polyacetals, and polyranging from brilliantto subdued, dull, or even 4 chalky appearance can be obtained. The process of this invention is not only more advantageously practiced than that of incorporating the delusterant in the preformed polymer, but the resulting products are also in general superior. These fibers compare favorably with previously described superpolyamide fibers (lustrous) in tenacity,

elasticity, resistance to solvents, aging qualities, etc., and are far superior to previously described delustered fibers, e. g. those of the cellulosic type,

in the above qualities. The low luster superpolyamide flowers because of their excellent tenacityand elasticity give low luster fabrics of excellent quality. An advantage of these fabrics over highly lustrous fabrics is that they tend to slenderize. When used in garments, for example, these fabrics yield an attractive dull appearance which tends to'slenderize the figure of the wearer. Furthermore, the delustered fibers have better hiding or covering power than the lustrous fibers. Delustered films, sheets, molded objects, etc. have similar advantages. Unique effects may be obtained by using the delustered fibers of this invention in conjunction with lustrous fibers.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof,-it is to be understood that I do not limit myself to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. A process for obtaining a homogeneous dispersion of polyamide and inert finely divided material, said process comprising heating a polyamide-forming composition under polymerizing conditions in the presence of about 0.1 to 5.0% by weight of inert finely divided pigment-like material which is incompatible with the polyamide resulting from said polyamide-forming composition and which is of different refractive index from that of said polyamide.

3. The process set forth in claim 1 in which said composition comprises a diamine and a compound of the class consisting of dicarboxylic acids and amide-forming derivatives of dibasic carboxylic acids.

4. The process set forth in claim 2 in whichsaid composition comprises a diainine of theformula NHzCHzRCHzNHz and a dicarboxylic'acid of the formula HOOCCHzRCHzCOOH, wherein R and R are saturated divalent hydrocarbon radicals and R has a chain length of at least two carbon atoms.

5. The process set-forth in claim 2 in which said polyamide-forming composition comprises hexamethylene diamine and adipic acid.

6. The process set forth in claim 2 in which said pigment-like materialis titanium dioxide.

7. The process set forth in claim 2 in which said polyamide forming composition comprises a polymerizable amino acid.

8. The process set forth in claim 2'in which said pigment-like material is barium sulfate.

GEORGE DE WITT GRAVES.

CERTIFICATE OF CORRECTION.

- Patent No. 2,20 ,722. June '2 191m.

GEORGE DE WITT GRAVES 'It is hereby certified that errorappears in the printed specification of the above numbered patent requiring correction as follows: Page 1, sec- 0nd. column, line 1+2, for the word "present" read -,presence-; page 5, second column, linelh, for l-9" read "LL- 5"; line 26, for "spinnert" read -spinneret--- page )4, second column, line 56, for "flowers" read --fibers---;

and that the said Letters Patent shouldbe read with this correction there-.

in that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 50th day of July, A. D. 1914.0.-

Henry Van Arsdale,

(Seal) Acting Commissioner of Patents. I 

